Most of the power sources used in today's portable electronic equipment are voltage sources such as batteries. Batteries provide most of their stored energy at a relative constant voltage. The important characteristic of a battery source is that the terminal voltage remains within a 20% window over 95% of the capacity discharge of the cell. Thus, almost all of the stored energy in a battery can be used at a relatively constant voltage.
A constant voltage, however, includes a ripple voltage. A ripple voltage is some amount of voltage variation about a steady voltage output value. Fixed value capacitors are typically used to reduce ripple voltage. The amount of ripple voltage is a function of stored energy discharged from a capacitor by the load impedance. To obtain the lowest ripple voltage the value of the capacitance is chosen as a maximum value practical for the application. However, the amount of energy or power consumed to get the desired operating level of voltage increases with the value of capacitance in other words, the larger the capacitance the longer delay in turn on cycle and the higher the power consumption. In addition, fixed value capacitors demonstrate a linear response in delivering their energy versus voltage drop. As can be seen in FIG. 1, the supply voltage of a fixed value capacitor declines linearly as the charge is removed therefrom. Therefore, as an energy transfer or voltage source, a fixed value capacitor has a significant percentage of energy which is unusable by the load due to the decrease in the supply voltage.
It is therefore desired to have a power supply with minimum ripple and without the detriments of the fixed value capacitors of the prior art.